I. Field of the Invention:
This invention relates generally to milling machine apparatus and more particularly to an improved end mill for use in such milling machines.
II. Discussion of the Prior Art:
Prior art end mills generally comprise a hardened steel shank having one or more helical convolutions or flutes extending from the tip thereof for a predetermined distance, the shank also including a smooth cylindrical portion which is adapted to fit into the end mill holding chuck on the milling machine. The strength and rigidity of end mills are very important factors in the overall productivity of milling machines. In prior art end mills, the depth of grinding of the flutes is uniform along the length of the end mill. On one hand, it is desirable that this depth be as large as possible so as to allow the chips generated during the milling process to be removed from the end mill. On the other hand, the deeper they are, the weaker the end mill will be due to the decrease of cross-sectional area. It is also desirable that the flutes be as long as possible to allow milling to greater depths. Milling to a depth greater than the flute length can cause the chips that are being removed from the workpiece to rise up the flute and become trapped between the end mill and the wall in the workpiece surrounding the milled-out area. The longer the flute is, though, the weaker the end mill will be. Prior art end mills, with uniform depths of grinding, are designed by compromising these design considerations, depending upon the end use of the tool. It can be shown that end mill breakage tends to occur at the transition between the fluted portion of the end mill and the straight or smooth portion. This is due to the fact that the forces acting on the end mill, when being fed through the workpiece, results in an increasing stress along the length of the end mill at increasing distances from the cutting end, assuming an end mill of uniform cross-sectional area.
I have devised a way of fabricating an end mill which is much less subject to breakage as compared to known prior art end mills. This permits faster feed rates during the milling operation, resulting in increased production and at lower cost, not only because of the potential increase in parts per unit of time, but also because of the savings in the cost of the end mills themselves, which are less costly to produce due to the decrease in the amount of material which must be removed by grinding during their fabrication. Moreover, my end mill design produces workpieces with smoother machined surfaces due to the greater stability and less chatter of the end mill in the chuck and the greater effective flute length. Then, too, the end mill of the present application can be used for making both shallow and deeper cuts, thus reducting the usual inventory of end mills of different sizes and lengths.